This invention relates to the fabrication of containers, for example, flexible sterilizable pouches intended for storing medical or surgical items. The invention is described in the context of such pouches, but the principles disclosed can be applied in other applications, as will be evident to those skilled in the art.
One form of pouch commonly used for storing sterile items, and for other uses, consists of two similarly sized rectangular sheets seamed to each other around their peripheries, using heat and pressure. If intended for gas sterilization (e.g. ethylene oxide or steam) one of the sheets is a made from a porous material which is permeable to the sterilizing gas, but is impermeable to bacteria and the like. This membrane could be, for example, surgical paper or a spun olefin (such as is sold by the DuPont Company under the trade name of Tyvek). The second sheet is usually a transparent non-porous plastic sheet, such as polyethylene, which is impervious to both gas and bacteria. In pouches intended for radiation sterilization, neither of the sheets need be porous; both can be polyethylene, or other suitable material.
A myriad of pouch constructions have been devised over the years, of which a great many are presently in commercial use. A number of examples of pouch designs can be found illustrated in U.S. Pat. Nos. 3,754,700, 4,367,816, 5,549,388, and 5,551,781, and in many other patents.
Whatever the style, pouches are usually made on a machine wherein the various required constituents of the pouch are supplied as webs from large rolls of the respective materials. As the materials are fed through the pouch making machine, the various webs which are used to create the pouch are brought into face to face contact, and the required peripheral and other seams are made. The seams are commonly made by pressing the areas to be seamed between a heated seaming iron (which has the form of the desired seam pattern) and a platen. Since it takes some time (generally between 0.5 and 1 second) to create a seam in this manner, the web feed is made intermittent. That is, the web feed is stopped during the time the seaming iron is pressing the web layers against the platen, and after each seaming is completed the web is then moved to bring the next area to be seamed under the seaming iron.
Other operations which may be needed to be performed on the materials making up the pouch, such as cutting openings in one or more webs, printing, etc., are synchronized with the seaming cycle. These operations may be accomplished while the seams are being formed, or while the web is being drawn between seamings, or in a combination of both.
As noted above, pouch seams are most commonly made by the application of heat and pressure to the seam areas, and the present invention is described herein as though that method is being used. Under some circumstances, however, it may be convenient to make some or all of the seams using adhesives rather than heat to cause the various films to adhere, and it will be appreciated that the principles of the present invention, as described below can be used to fabricate pouches using adhesive technology in place of heat and pressure.
After the needed peripheral and possibly other seams are made, a fresh web area is moved under the seaming iron, and the previously seamed area is moved to a cutoff knife where the completed pouches are severed from the web. The cutoff knife is not usually located immediately adjacent the seaming iron. For practical space reasons, normally there are one or more patterns of perimeter seams between the seaming iron and the cutoff knife, and one or more additional seaming cycles usually occur between the time a seam is made and the time that the just seamed section arrives at the cutoff knife.
Cutoff knives generally operate much faster than do the seaming irons; for example, even before the present invention, knives operating at a rate of five cuts per second or even somewhat faster were available. The cutoff cycle in prior art pouch making machines is also synchronized with the seaming cycle.
In order to achieve relatively high production, it is common to utilize seaming iron assemblies which can make the seams for many (for example, 10 or more) pouches at a time along the length of the web. Hence, in such a machine, pouches are made in two consecutive timewise steps: 1) seaming a plurality of pouches simultaneously, and 2) sequentially cutting off completed pouches. Assuming a seaming iron ten pouches deep, if it takes one second to make the seams for the ten pouches, it will take about an additional two seconds to cut the pouches off the web (at a rate of five per second), for a total of three seconds to make the ten pouches. This is a theoretical rate of 200 pouches per minute. If the seaming iron were twenty pouches deep, the theoretical production would be 240 pouches per minute. The maximum possible theoretical production, even if the seaming iron were an infinite number of pouches deep, would be 300 pouches per minute, being limited by the cutoff rate of prior art cutoff knives (about 5 cuts per second). In a copending application by the present inventor (U.S. patent application Ser. No. 08/824,817) means are disclosed which permits a production rate up to the capacity of the cutoff knife, even though the seaming iron is not of infinite length.
The present invention improves the rate of production of pouch making machines by 1) providing a cutoff knife which can operate at a much faster rate than prior art knives, 2) not stopping the web while severing the pouches (i.e., causing the cutoff knife to travel with the web during the severing operation), and 3) permitting the cutting off of the completed pouches to proceed even while the web is stationary in the seam forming portion of the machine (while the seams are being created).
It is an object of the present invention to provide a pouch fabricating machine and method which improves on the production rate obtainable with prior art pouch fabricating machines.
It is another object of the present invention to provide a web cutting knife capable of much higher cutoff rates when compared to prior art knives.